The invention relates to a method of and to an apparatus for establishing and maintaining dispersions of liquid and gaseous fractions, particularly for dispersing oxygen, air and/or other oxygen-containing gases in liquid sludge and/or sewage. More particularly, the invention relates to improvements in methods and apparatus which can be utilized to carry out biochemical processes involving intimate contact of liquid fractions with gaseous fractions and/or microorganisms in a reactor, preferably in an upright vessel.
It is known to disperse a gaseous fraction in a liquid fraction and to cause the resulting dispersion to flow upwardly in a vessel wherein the liquid fraction is discharged at the top and the spent gaseous fraction which becomes separated from the liquid fraction is evacuated at the top independently of the treated liquid fraction. An apparatus which can be used for the practice of such method is disclosed in German patent application Ser. No. P 35 36 057.7. An advantage of such apparatus is that the period of dwell of the dispersion therein is relatively long even though the vessel is relatively short. The apparatus of this application comprises an inlet for admission of the dispersion into and substantially tangentially of the lower portion of the vessel, and a conduit which returns a portion of or the entire dispersion from the upper portion into the lower portion of the vessel for recirculation, i.e., for longer-lasting contact of the liquid and gaseous fractions. Intensive contact between the liquid and gaseous fractions is of particular importance if the apparatus is used as a means for initiating and promoting biochemical reactions, especially reactions of air and/or other oxygen-containing gases with active biomasses in a liquid medium. Such intensive contact contributes to the economy of the operation by ensuring that the treatment is completed within a relatively short interval of time and that the admitted gaseous fraction is utilized with a high degree of effectiveness. Moreover, it is relatively simple to maintain the temperature of the dispersion at an optimum value. All this is ensured by maintaining the gaseous fraction in desirable intimate contact with the liquid or liquefied fraction for a sufficiently long interval of time.
The method and apparatus of the aforementioned German application are simple and effective. However, it has been found that the path along which the dispersion rises in the vessel is often too short unless the height of the vessel is unduly increased. This is due to the fact that friction-induced deceleration of the dispersion in the vessel entails a pronounced reduction of the rate and intensity of circulation already at a level rather close to the inlet of the vessel. Moreover, the decelerated gaseous and liquid fractions exhibit a pronounced tendency to become separated from each other. As the tendency of the dispersion to circulate decreases or vanishes, the dispersion begins to flow upwardly along a more or less straight path so that the period of dwell in the vessel and hence the reaction times ar reduced accordingly.